I always use 23x1.5 3cc , the first pin I ever used a few years back was huge!!(I think it was 18) anyway, 21 shouldn't be to bad, I would use it as long as it was 1.5
I bought some 21ga, 1" monojects. When I saw them, I thought `shit, this is gonna hurt'. But I had no pinch or pain at all and the oil flowed a lot easier than the 23ga.
just because you dont see a 21 gauge doing any damage or feel it doing any damage, it does not mean it isnt. Go with the smallest pin available and drop the I use 20gauge attitude because it worked for me before stuff
I love 21's for oil based. they draw quick and they inject smoothly. Just make sure you have a steady hand... or else you are in for some pain. I like 23's... but I will use a 21 anyday!!! Have no fear.
DBaller